breakfast, lunch, dinner

In South Korea, when someone meets a friend, instead of asking, “How are you?” Koreans tend to ask, “Have you eaten?”

The reason is that Koreans are convinced that hunger is related to mood, and because they also believe that missing a meal (breakfast, lunch, dinner) is a bad omen.

If you answer his question with “no,” he will leave you and not talk to you because you are in a bad mood, or at least he will bring you food if he wants to talk to you about an important matter.
The history of this phrase dates back to the early 1950s, after the Korean War. Because of the famine, the question was, “Have you eaten?” - Out of genuine concern for a person’s well-being, if he answers yes, this is a sign that he is fine.